PROKARYOTES AND EUKARYOTES_Presentation001.pptx

Prokaryotes (bacteria and blue-green algae) are the most abundant organisms on earth.
A prokaryotic cell does not contain a membrane-bound nucleus.
Bacteria are either cocci, bacilli or spirilla in shape, and fall into two groups, the eubacteria and the archaebacteria.
Each prokaryotic cell is surrounded by a plasma membrane.
The cell has no subcellular organelles, only infoldings of the plasma membrane called mesosomes.
The deoxyribonucleic acid (DNA) is condensed within the cytosol to form the nucleoid.
Some prokaryotes have tail-like flagella.
Eukaryotic cells have a membrane-bound nucleus and a number of other
membrane-bound subcellular (internal) organelles, each of which has a specific function.
The plasma membrane surrounds the cell, separating it from the external
environment.
The plasma membrane is a selectively permeable barrier due to
the presence of specific transport proteins.
It is also involved in receiving
information when ligands bind to receptor proteins on its surface, and in the processes of exocytosis and endodocytosis.

The nucleus stores the cell’s genetic information as DNA in chromosomes.
It is bounded by a double membrane but pores in this membrane allow molecules to move in and out of the nucleus.

The nucleolus within the nucleus is the site of ribosomal ribonucleic acid (rRNA) synthesis.
This interconnected network of membrane vesicles is divided into two distinct parts.
The rough endoplasmic reticulum (RER), which is studded with
ribosomes, is the site of membrane and secretory protein biosynthesis and
their post-translational modification. The smooth endoplasmic reticulum (SER) is involved in phospholipid biosynthesis and in the detoxification of toxic compounds.

The Golgi apparatus, a system of flattened membrane-bound sacs, is the
sorting and packaging center of the cell.
It receives membrane vesicles from
the RER, further modifies the proteins within them, and then packages the
modified proteins in other vesicles which eventually fuse with the plasma
membrane or other subcellular organelles.

Mitochondria have an inner and an outer membrane separated by the
intermembrane space.
The outer membrane is more permeable than the inner membrane due to the presence of porin proteins. The inner membrane, which is folded to form cristae, is the site of oxidative phosphorylation, which produces ATP. The central matrix is the site of fatty acid degradation and the citric acid cycle.

Chloroplasts in plant cells are surrounded by a double membrane and have an internal membrane system of thylakoid vesicles that are stacked up to form grana.
The thylakoid vesicles contain chlorophyll and are the site of photosynthesis. Carbon dioxide (CO2) fixation takes place in the stroma, the soluble matter around the thylakoid vesicles.

Lysosomes in animal cells are bounded by a single membrane. They have an
acidic internal pH 4–5 maintained by proteins in the membrane that
pump in H+ ions. Lysosomes contain acid hydrolases

1. PROKARYOTES . And . Eukaryotes

2. PROKARYOTES

3. Prokaryotes are the most numerous and widespread organisms on earth. They have no defined membrane-bound nucleus. Prokaryotes range in size. Four basic shapes: spherical (cocci), rodlike (bacilli) helically coiled ( spirilla ) comma (vibrio)

4. They can be divided into two separate groups: the eubacteria and the archaebacteria. The eubacteria are the common bacteria in soil, water and living in or on larger organisms, and include the Gram-positive and Gram-negative bacteria and cyanobacteria (photosynthetic blue-green algae). The archaebacteria grow in unusual environments such as salt brines, hot acid springs and in the ocean depths, and include the sulfur bacteria and the methanogens.

5. Cell structure A prokaryotic cell is bounded by a plasma membrane that completely encloses the cytosol and separates the cell from the external environment. The plasma membrane, which is about 8 nm thick, consists of a lipid bilayer containing proteins.

6. Plasma membrane may be infolded to form mesosomes . The mesosomes may be the sites of deoxyribonucleic acid (DNA) replication and other specialized enzymatic reactions. In photosynthetic bacteria, the mesosomes contain the proteins and pigments that trap light and generate adenosine triphosphate (ATP).

7. The aqueous cytosol contains the macromolecules [enzymes, messenger ribonucleic acid (mRNA), transfer RNA ( tRNA ) and ribosomes], organic compounds and ions needed for cellular metabolism. In prokaryotes, chromosome possess single circular molecule of DNA which is condensed to form nucleoid. Many bacterial cells have one or more tail-like appendages called flagella which are used to move the cell through its environment.

8. To protect the cell from mechanical injury and osmotic pressure, possess thick cell wall. The cell wall composed of peptidoglycan, a complex of oligosaccharides and proteins.

9. The oligosaccharide component consists of linear chains of alternating N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (NAM) linked attached via an amide bond to the lactic acid group on NAM is a D-amino acid-containing tetrapeptide. Adjacent parallel peptidoglycan chains are covalently cross-linked through the tetrapeptide side-chains by other short peptides. This cross-linking in the peptidoglycan cell wall gives it its strength and rigidity.

10. The (1–4) glycosidic linkage between NAM and GlcNAcvis susceptible to hydrolysis by the enzyme lysozyme which is present in tears, mucus and other body secretions. The presence of D-amino acids in the peptidoglycan, resistant to the action of proteases which act on the more commonly occurring L-amino acids but provides a unique target for the action of certain antibiotics such as penicillin. Penicillin acts by inhibiting the enzyme that forms the covalent cross-links in the peptidoglycan, thereby weakening the cell wall.

11. Bacteria can be classified as either Gram-positive or Gram-negative depending on whether or not they take up the Gram stain. Gram-positive bacteria have a thick cell wall surrounding their plasma membrane, whereas Gram-negative bacteria (e.g. Escherichia coli) have a thinner cell wall and a second outer membrane. In contrast, outer membrane is very permeable to the passage of large molecules. Porin proteins which form pores in the lipid bilayer. Between the outer membrane and the cell wall is the periplasm .

12. EUKARYOTES

13. A eukaryotic cell consist of plasma membrane, has a membrane bound nucleus and contains a number of other distinct subcellular organelles. Organelles are membrane-bounded structures, each having a unique function and each containing a specific complement of proteins and other molecules. Animal and plant cells have the same basic structure, although some organelles and structures are found in one and not the other. For example, chloroplasts, vacuoles and cell wall are present in plant cells, while lysosomes in animal cells).

14. The plasma membrane envelops the cell, creating boundary from the external environmemt membrane. It also helps in maintaining the correct ionic composition and osmotic pressure of the cytoplasm. The plasma membrane, like all membranes, is impermeable to most substances but the presence of specific proteins in the membrane allows certain molecules to pass through, therefore making it selectively permeable. Involved in communicating with other cells, in particular through the binding of ligands (small molecules such as hormones, neurotransmitters, etc.) to receptor proteins on its surface. The plasma membrane is also involved in the exocytosis (secretion) and endocytosis (internalization) of macromolecules.

15. Nucleus The nucleus is bounded by two membranes, the inner and outer nuclear membranes. These two membranes fuse together at the nuclear pores through which molecules [messenger ribonucleic acid (mRNA), proteins, ribosomes, etc.] can move between the nucleus and the cytosol. Other proteins, for example those involved in regulating gene expression, can pass through the pores from the cytosol to the nucleus. The outer nuclear membrane is often continuous with the rough endoplasmic reticulum (RER). Within the nucleus the DNA is tightly coiled around histone proteins and organized into complexes called chromosomes. Visible under the light microscope is the nucleolus, a subregion of the nucleus which is the site of ribosomal ribonucleic acid ( rRNA ) synthesis

16. Endoplasmic reticulum The endoplasmic reticulum (ER) is an interconnected network of membrane reticulum vesicles. The rough endoplasmic reticulum (RER) is studded on the cytosolic face with ribosomes, the sites of membrane and secretory protein biosynthesis. Within the lumen of the RER are enzymes involved in the post-translational modification (glycosylation, proteolysis, etc.) of membrane and secretory proteins. The smooth endoplasmic reticulum (SER), which is not studded with ribosomes, is the site of phospholipid biosynthesis, and is where a number of detoxification reactions take place.

17. Golgi apparatus The Golgi apparatus, a system of flattened membrane-bound sacs, is the sorting center of the cell. Membrane vesicles from the RER, containing membrane and secretory proteins, fuse with the Golgi apparatus and release their contents into it. On transit through the Golgi apparatus, further post-translational modifications to these proteins take place and they are then sorted and packaged into different vesicles. These vesicles bud off from the Golgi and are transported through the cytosol, eventually fusing either with the plasma membrane to release their contents into the extracellular space (a process known as exocytosis; see Topic E4) or with other internal organelles (lysosomes, peroxisomes, etc.).

18. Mitochondria A mitochondrion has an inner and an outer membrane between which is the intermembrane space. The outer membrane contains porin proteins which make it permeable to molecules of up to 10 kDa . The inner membrane, which is considerably less permeable, has large infoldings called cristae which protrude into the central matrix. The inner membrane is the site of oxidative phosphorylation and electron transport involved in ATP production. The central matrix is the site of numerous metabolic reactions including the citric acid cycle and fatty acid breakdown. Within the matrix is found the mitochondrial DNA which encodes some of the mitochondrial proteins.

19. Chloroplasts Chloroplasts also have inner and outer membranes. In addition, there is an extensive internal membrane system made up of thylakoid vesicles (interconnected vesicles flattened to form discs) stacked upon each other to form grana. Within the thylakoid vesicles is the green pigment chlorophyll, along with the enzymes that trap light energy and convert it into chemical energy in the form of ATP. The stroma, the space surrounding the thylakoid vesicles, is the site of carbon dioxide (CO2) fixation – the conversion of CO2 into organic compounds. Chloroplasts, like mitochondria, contain DNA which encodes some of the chloroplast proteins.

20. Lysosomes Lysosomes, which are found only in animal cells, have a single boundary membrane. The internal pH of these organelles is mildly acidic (pH 4–5), and is maintained by integral membrane proteins which pump H+ ions into them. The lysosomes contain a range of hydrolases that are optimally active at this acidic pH (and hence are termed acid hydrolases) but which are inactive at the neutral pH of the cytosol and extracellular fluid. These enzymes are involved in the degradation of host and foreign macromolecules into their monomeric subunits; proteases degrade proteins, lipases degrade lipids, phosphatases remove phosphate groups from nucleotides and phospholipids, and nucleases degrade DNA and RNA. Lysosomes are involved in the degradation of extracellular macromolecules that have been brought into the cell by endocytosis.

21. Peroxisomes These organelles have a single boundary membrane and contain enzymes that degrade fatty acids and amino acids. A byproduct of these reactions is hydrogen peroxide, which is toxic to the cell. The presence of large amounts of the enzyme catalase in the peroxisomes rapidly converts the toxic hydrogen peroxide into harmless H2O and O2:

22. Cytosol The cytosol is that part of the cytoplasm not included within any of the subcellular organelles, and is a major site of cellular metabolism. It contains a large number of different enzymes and other proteins. The cytosol is not a homogenous ‘soup’ but has within it the cytoskeleton, a network of fibers criss-crossing through the cell that helps to maintain the shape of the cell. The cytoskeletal fibers include microtubules (25 nm in diameter), intermediate filaments (10 nm in diameter) and microfilaments (8 nm in diameter). Also found within the cytosol of many cells are inclusion bodies (granules of material that are not membrane-bounded) such as glycogen granules in liver and muscle cells, and droplets of triacylglycerol in the fat cells of adipose tissue.

23. Cytoskeleton In the cytosol of eukaryotic cells is an internal scaffold, the cytoskeleton. The cytoskeleton is important in maintaining and altering the shape of the cell, in enabling the cell to move from one place to another, and intransporting intracellular vesicles. Three types of filaments make up the cytoskeleton: microfilaments, intermediate filaments and microtubules. The microfilaments, diameter approximately 7 nm, are made of actin and have a mechanically supportive function.

24. Through their interaction with myosin, the microfilaments form contractile assemblies that are involved in various intracellular movements such as cytoplasmic streaming and the formation of membrane invaginations. The intermediate filaments (7–11 nm in diameter) are probably involved in a load-bearing function within the cell. For example, the skin in higher animals contains an extensive network of intermediate filaments made up of the protein keratin that has a two-stranded alpha-helical coiled-coil structure.

25. Microtubules The third type of cytoskeletal filaments, the microtubules, are hollow cylindrical structures with an outer diameter of 30 nm that are built from the protein tubulin. The rigid wall of a microtubule is made up of a helical array of alternating alpha and beta tubulin subunits, each of 50 kDa . A cross-section through a microtubule reveals that there are 13 tubulin subunits per turn of the filament. Microtubules in cells are formed by the addition of alpha and beta tubulin molecules to pre-existing filaments or nucleation centers

26. Plant cell wall Surrounding the plasma membrane of a plant cell is the cell wall, which imparts strength and rigidity to the cell. This is built primarily of cellulose, a rod-like polysaccharide of repeating glucose units linked. These cellulose molecules are aggregated together by hydrogen bonding into bundles of fibers, and the fibers in turn are cross-linked together by other polysaccharides. In woody plants another compound, lignin, imparts added strength and rigidity to the cell wall. Lignin is a complex water-insoluble phenolic polymer.

27. Plant cell vacuole Plant cells usually contain one or more membrane-bounded vacuoles. These are used to store nutrients (e.g. sucrose), water, ions and waste products (especially excess nitrogen-containing compounds). Like lysosomes in animal cells, vacuoles have an acidic pH maintained by H+ pumps in the membrane and contain a variety of degradative enzymes. Entry of water into the vacuole causes it to expand, creating hydrostatic pressure (turgor) inside the cell which is balanced by the mechanical resistance of the cell wall.

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